This invention pertains to electric lamps and, more particularly, is concerned with electric lamps of the beam mode variety.
Beam mode lamps utilize anode and cathode discharge electrodes to form an electron beam. The discharge electrodes are arranged so that the electric beam extends beyond the anode into a drift region. The electrodes and drift region are within the volume of a transparent envelope. An excitable fill material permeates the volume and emits ultraviolet radiation when excited by the electron beam. The ultraviolet radiation can be converted to visible radiation by a phosphor coating upon the envelope.
When it was first conceived, the beam mode lamp was a DC device with an operating voltage of about 20 volts. In order for this lamp to be operated from common 120 AC line voltage, it is necessary to supply a step down transformer and a full wave rectifier.
An improved beam mode lamp described in co-pending application Ser. No. 337,046, filed Jan. 4, 1982, for "Dual Cathode Beam Mode Fluorescent Lamp" has two discharge electrodes which alternate their functions as cathode and anode. This arrangement allows the lamp to operate on AC voltage without a rectifier. A step down transformer or the like is still necessary, however. It is manifestly desirable to provide a dual cathode beam mode lamp which may be operated directly at line voltage without the need of a step down transformer.